The 340 employees at the coal-fired energy plant remain on the job, however.

“All of them are continuing to report to work, taking the opportunity to perform plant maintenance tasks,” said FirstEnergy spokeswoman Stephanie Walton.

What’s not clear is how long the plant will be down. Walton said the plant’s 2,940-megawatts of capacity are available to the regional grid operator, PJM Interconnection, should it end up needed, and FirstEnergy is monitoring the pricing situation. Walton declined to discuss the impact of the plant’s shutdown on coal deliveries.

Walton said the temporary idling does not change FirstEnergy’s plans to revamp the plant in what it said in October 2015 was a $260 million upgrade that will help it comply with environmental regulations. The centerpiece of that is a coal-ash dewatering facility, which takes care of residual waste in the coal-burning process.

“We remain committed to the Bruce Mansfield Plant and none of our future plans for the facility have changed,” she said. “We are continuing to construct the dewatering facility so the plant can operate for many years to come.”